The present invention relates to fluid control valve systems adapted to govern fluid power operation of a plurality of fluid actuators, and it more particularly relates to an improved use of main relief valves in such systems.
In fluid control valve systems a first hydraulic actuator, for example, may govern power steering of an articulated vehicle, and a second actuator may govern operation of an implement on the vehicle. A directional control valve is used for control of the power steering in combination with a pressure compensating valve, which gives the power steering priority when a single source of fluid supply is used for actuating both the power steering and the implement. In systems for governing the operation of a plurality of fluid devices from a single source of fluid supply, it is general practice to protect the supply by a main relief valve upstream from a first directional control valve as disclosed in the Tennis U.S. Pat. No. 3,722,543, and to permit operation of a second actuator in case of stalling of a first actuator by control of a pressure compensator for the first actuator as disclosed in my U.S. Pat. No. 3,911,942. It has been found that sudden pressure changes in these systems, particularly when used for power steering, can cause shifting of metering lands of a compensating spool, with a resulting undesirable sudden change in fluid flow.
An object of the present invention is to provide a fluid control valve system which substantially obviates one or more of the limitations of the described prior art systems.
Another object of the present invention is to simplify fluid control valve systems by eliminating the need for a plurality of fluid power sources for smoothly and efficiently operating a plurality of actuators on an articulated vehicle.
Other objects, purposes and characteristic features will be in part obvious from the accompanying drawing, and in part pointed out as the description of the invention progresses.